Ball joint, in particular steering or suspension ball joint for motor vehicles and, method for making a bearing for same

ABSTRACT

A ball joint, and in particular a motor vehicle steering or suspension ball joint, which includes a pivot with a spherical head, a ball joint case with a housing for receiving the pivot head and a case housing, and a plastic bearing interposed between the pivot head and the case housing. The ball joint bearing includes a cup molded in one single piece, closed at a base, and having a molded inner spherical surface extending over more than one hemisphere. A circular orifice with a diameter smaller than the spherical inner surface diameter, opposite the base, is also provided as are several rupture zones distributed on the periphery of the opening part and shaped so as to be subjected to a predefined rupture into two sections when the opening part first expands and to enable, after the head has been inserted in the bearing, an elastic tightening of the opening part with accurate repositioning of the two sections of each rupture zone around the head.

The present invention relates to a ball joint, especially a steering orsuspension ball joint for motor vehicles, comprising a pivot providedwith a spherical head, a ball-joint case provided with a housing forreceiving the said pivot head, and a bearing shell of plastic materialinterposed between the pivot head and the case housing.

The invention also relates to a process for manufacture of a bearingshell for such a ball joint.

Ball joints comprising a bearing shell of plastic material are known.

According to U.S. Pat. No. 5,152,628 (=German Patent A 4032541), abearing shell in the form of a spherical zone extending on both sides ofthe equator is provided on one side of the equator with a plurality ofmeridian slits which limit plastic deformation of the bearing shellduring mounting of the spherical head of the pivot in the bearing shellby expansion of the part equipped with slits. Nevertheless, these slitshave an unfavorable influence on the lubrication of the pivot. In fact,these slits exhibit rough areas and excessive thicknesses derived fromthe method for manufacture of the bearing shell, leading to excessivepressures and in turn an increase in the friction of the ball joint.

According to European Patent A 0653573, a bearing shell is molded in theform of a hemispherical cup, which is prolonged on its orifice side by acylindrical skirt which, during assembly of the ball joint, is deformedplastically into a spherical segment by a locking ring of the balljoint. This does not allow control of the friction, and so largevariations of the friction moment occur during mounting, during thefirst displacements of the pivot and throughout the entire operation ofthe ball joint.

For all of these reasons, the known ball joints are not satisfactoryand, when used as steering ball joints, for example, lead todeterioration of the return movement of the steering, of centeringaround the mean position, of driving comfort and even of steeringresponse.

The object of the present invention is a ball joint which isdistinguished from known ball joints both by a reduction of friction andby a reduction of the variations of the friction moment under radial andaxial load, of elasticity and of wear, throughout the entire life of theball joint.

The ball joint which is the object of the invention comprises a pivotprovided with a spherical head, a ball-joint case provided with ahousing to receive the said pivot head, and a bearing shell of plasticmaterial interposed between the pivot head and the case housing. Thebearing shell of the ball joint comprises a one-piece molded cup, closedat the bottom side and provided, by molding,

with a spherical inside surface extending over a solid anglecorresponding to more than one hemisphere,

with a circular orifice, whose diameter is smaller than the diameter ofthe spherical inside surface, opposite the bottom, and

with a plurality of rupture zones of small thickness distributed overthe circumference of the orifice part, while extending from the saidorifice toward the equatorial plane of the spherical surface disposedparallel to the plane of the said orifice, the said rupture zones havingsuch a conformation that each undergoes predefined rupture into twosections during a first expansion of the orifice part and that, afterinsertion of the pivot head into the bearing shell, elastic constrictionof the orifice part is permitted together with exact repositioning ofthe two sections of each rupture zone around the pivot head.

The provision of rupture zones makes it possible to mold the bearingshell in the form of a cup having a continuous spherical inside surfacewhile remedying the drawbacks resulting, in the known ball joints, fromthe presence of the slits needed to permit assembly of the ball joint orplastic deformations occurring during assembly.

Preferably the rupture zones have a conformation that each gives rise toa rupture along a zig-zag line, predefined by a corresponding line ofweakness.

To obtain a ball joint with a predefined friction and damping effect,the bearing shell can be provided on the outside, in the equatorialzone, with a cylindrical part, which toward the bottom zone is followedby a substantially conical part. In corresponding manner, the housing ofthe case is provided with a cylindrical part followed by a substantiallyconical bottom part.

Preferably the conical part at the bottom of the housing of the case cancomprise a frustoconical outside zone, with a taper angle larger thanthe taper angle of the conical part of the bottom zone of the bearingshell and a conical inside (central) zone with a taper angle smallerthan the taper angle of the said conical outside part of the bearingshell.

Preferably the bearing shell is provided, between its cylindricaloutside part and its orifice, with a frustoconical outside part followedat the level of the orifice by an outside shoulder. The ball jointadditionally comprises a locking ring which is provided with afrustoconical inside surface corresponding to the said frustoconicaloutside part of the bearing shell, and which, after insertion of thepivot head into the bearing shell, can be interlocked behind theshoulder of the bearing shell so as to maintain the assembled pivot andbearing shell in the form of a module capable of being mounted as suchin the case of the ball joint and of being fixed therein, for example bycrimping. By the dimensioning of this locking ring, it is possibleperfectly to control the play between the bearing shell and the pivot ofthe ball joint.

The bearing shell of the ball joint according to the invention can bemanufactured by advantageously molding the bearing shell between a fixedmold part whose cavity corresponds at least to the bottom part of thebearing shell, at least one movable mold part whose cavity correspondsat least to the orifice part of the bearing shell, and a movable corewith spherical head, whose shape corresponds substantially to the shapeof the spherical head of the pivot of the ball joint. To remove thebearing shell from the mold, there are successively displaced

a) the movable mold part, to release the orifice part of the bearingshell, or in other words the part comprising the rupture zones, towardthe outside, and

b) the movable core, to extract the spherical head of the bearing shellon the orifice side, while causing well-defined rupture of the saidrupture zones by expansion of the orifice part of the bearing shell.

Preferably the bearing shell is blocked in the fixed part of the moldduring extraction of the spherical head of the core.

An illustrative and non-limitative practical example of a ball jointaccording to the invention and a practical example of the process formanufacture of the bearing shell of this ball joint will be described inmore detail hereinafter with reference to the attached drawings,wherein:

FIG. 1 is an axial section of a ball joint according to the invention;

FIG. 2 is an axial section of the bearing shell of the ball joint ofFIG. 1;

FIG. 3 is an outside view of the bearing shell of FIG. 2;

FIGS. 4 to 9 represent cross-sectional views of the sequences of removalof the bearing shell according to FIGS. 2 and 3 from the mold.

The ball joint illustrated by FIG. 1, for example a steering ball joint,comprises a pivot 1 whose spherical head 2 is mounted movably to rotatearound its axis and to pivot (as represented by broken lines) in ahousing 3 of a ball-joint case 4. A bearing shell 5 of plastic materialis interposed between head 2 of pivot 1 and housing 3 of case 4, and alocking ring 6 maintains the assembly of head 2 and bearing shell 5 inhousing 3 of case 4. An elastic bellows 7 fixed at one end to ring 6 andat the other end to pivot 1, between head 2 and a threaded joint base 8of pivot 1, isolates the assembly of head 2 and bearing shell 5 from theoutside, to prevent ingress of extraneous material and loss oflubricant.

As shown in FIGS. 2 and 3, bearing shell 5 has substantially the form ofa cup, with a spherical inside surface 9, which as the case may be canbe provided with a plurality of hollows or depressions 10 forminglubricant reservoirs. Spherical inside surface 9 extends over a solidangle corresponding to more than one hemisphere, or approximately 3 π inthe illustrated example under consideration. Opposite its closed bottompart 11, bearing shell 5 is provided with a circular orifice 12 ofdiameter smaller than the diameter of spherical inside surface 9.Bearing shell 5 is prolonged beyond orifice 12 by a substantiallycylindrical part 13, which is terminated by an outside shoulder 14having a chamfered profile on the inside and outside.

Prolongation 13 and shoulder 14 are interrupted by three notches 15distributed at 120° relative to one another. Each notch 15 is prolongedtoward bottom part 11 by a zone 16 of reduced thickness provided, at themiddle of its width, with a well-defined rupture line 17, for example azig-zag line of weakness.

On the outside, bearing shell 5 is provided in succession, betweenprolongation 13 and bottom part 11, with a frustoconical part 18, acylindrical part 19 and a conical part 20 having a taper angle γ.

Zones 16 of reduced thickness are formed on the outside, or in otherwords from the outside surface toward the inside surface, acrossfrustoconical part 18 as far as cylindrical part 19, up to a shortdistance from the equatorial plane parallel to orifice 12, withoutaffecting inside surface 9 of bearing shell 5, as is shown in particularin FIG. 2.

In addition, bearing shell 5 is provided on the outside, in cylindricalpart 19, with a plurality of hollows or pockets 21, whose function isrelated to the process for manufacture of bearing shell 5, describedhereinafter.

Housing 3 of ball-joint case 4 according to FIG. 1 has a shape matchedto the outside shape of bearing shell 5. In the present case, housing 3comprises mainly a part of cylindrical surface 22 corresponding tocylindrical part 19 of bearing shell 5, and a frustoconical bottomsurface 23 matched to conical surface 20 of bottom 11 of bearing shell5. It should be noted that frustoconical bottom surface 23 surrounds acentral part 24, whose taper angle ε is smaller than the taper angle ofremaining part 23, and therefore smaller than taper angle γ of outsidesurface 20 of bottom 11 of bearing shell 5.

Locking ring 6, which is shown in FIG. 1, is assembled together withbearing shell 5 after spherical head 2 of pivot 1 has been placed inbearing shell 5. Placement of the head in bearing shell 5 necessitatesexpansion of bearing shell 5 in its orifice part, or in other words thepart comprising frustoconical outside part 18, prolongation 13 andshoulder 14. This expansion is possible after rupture of rupture zones16 at the position of weakness zones 17, these ruptures giving the partssituated between rupture lines 16 sufficient elasticity to undergoelastic expansion as far as the diameter of spherical head 12.

Once spherical head 2 of pivot 1 has been placed in bearing shell 5,locking ring 6 is snapped in behind shoulder 14 of prolongation 13, thissnap-in operation being facilitated by frustoconical inside surface 25of locking ring 6, with taper angle corresponding to the taper angle offrustoconical outside part 18 of bearing shell 5.

It is important to note that the inside diameter of locking ring 6 ispreferably slightly smaller than the outside diameter of prolongation 13of bearing shell 5. By this fact, while locking ring 6 is being snappedin on bearing shell 5 enclosing spherical head 2 of pivot 1, ring 6exerts a radial clamping action on prolongation 13, which leads toconstriction of bearing shell 5 around head 2, such that the taper angleof conical outside surface 20 of the bottom of bearing shell 5 decreasesslightly. This constriction has the effect of preventing any playbetween head 2 of pivot 1 and bearing shell 5 on the ball-joint modulecomprising pivot 1, bearing shell 5 and locking ring 6 assembledtogether, before this module is mounted in ball-joint case 4.

Finally, the ball-joint module comprising pivot 1, bearing shell 5surrounding spherical head 2 of pivot 1, as well as locking ring 6snapped in around the orifice part of bearing shell 5, is mounted inball-joint case 4, the outside shape of bearing shell 5 assuming theshape of housing 3 of case 4, and fixation ring 6 is fixed to case 4 bycrimping an inside shoulder 26 of case 4 onto an outside collar 27 oflocking ring 6.

During crimping of the module into ball-joint case 4, a thrust (towardthe bottom in FIG. 1) is exerted on pivot 1. Depending on the magnitudeof this thrust, it is possible to control the deformation that bearingshell 5 undergoes in its bottom zone 11, by the fact of the particularconformation of bottom zone 23, 24 of housing 3, and thereby toestablish friction and damping of the ball joint, while eliminating anyradial and axial play.

FIGS. 4 to 9 illustrate a process for manufacture of bearing shell 5,making it possible directly to obtain bearing shell 5 together with itsalready broken rupture zones 16.

According to FIG. 4, bearing shell 5 as illustrated by FIGS. 2 and 3 ismolded in an injection-molding machine 30 comprising a fixed mold platen31 which forms the outside surface of bottom part 11 and a part ofcylindrical zone 19, a movable mold platen 32, which forms the remainingoutside surface (remaining part of cylindrical zone 19, frustoconicalpart 18 with rupture zones 16, prolongation 13, shoulder 14), a movablemold platen 33, which forms the inside surface of prolongation 13 and ofshoulder 14, and a movable core 34 comprising a spherical head 35 whichforms spherical inside surface 9 of bearing shell 5. There are alsoshown a plurality of slides 36 mounted to be movable in radialtranslation in fixed mold platen 31 and controlled by a movable blockingplaten 37, and ejectors 38 mounted to be movable in axial translation inplaten 31.

Movable mold platens 32, 33, movable core 34 and movable blocking platen37 are mounted to slide on uprights 39, movable platens 32, 33 andmovable core 34 being connected in such a way that an action on one ofthese elements, in the present case on mold platen 33, at 40, in thedirection of opening of injection-molding machine 30, toward the rightin FIG. 4, causes a sequence of phases of removal from the moldaccording to FIGS. 5, 6, 7, before two sequences of unblocking andejection according to FIGS. 8 and 9.

According to FIG. 5, only movable mold platen 33 is displaced toward theright, following a first stroke applied at 40.

According to FIG. 6, the two mold platens 33 and 32 are displacedsimultaneously toward the right, following a second stroke applied at40.

According to FIG. 7, the two movable mold platens 32, 33 and movablecore 34 are displaced simultaneously to the right, following a thirdstroke applied at 40. Since bearing shell 5 is retained in fixed moldplaten 31 by slides 36 maintained in blocking position by blockingplaten 37, the displacement of head 35 of core 34 causes expansion ofthe orifice part of bearing shell 5 and consequently rupture at theposition of rupture zones 16, thus giving the parts situated betweenrupture zones 16 sufficient elasticity to permit elastic expansion toallow removal of head 35.

According to FIG. 8, the displacement of movable blocking platen 37toward the left permits slides 36 to be disengaged radially toward theoutside, to release bearing shell 5.

Finally, according to FIG. 9, ejectors 38 eject bearing shell 5 releasedby slides 36 from fixed mold platen 31.

The process of removal from the mold with rupture as represented anddescribed makes it possible to obtain a bearing shell which, as soon asit has been removed from the mold, is ready to receive the sphericalhead of a ball-joint pivot for the purpose of making a ball-joint modulecomprising the ball-joint pivot, the bearing shell and the locking ringin assembled form, this module being capable of being mounted as such inthe ball-joint case.

By virtue of the control of friction and damping that the ball jointaccording to the invention permits by the design and geometry of thebearing shell and by the process for manufacturing same, as aconsequence of the perfect adjustment of the inside contour of thebearing shell to the spherical head of the pivot and of the outsidecontours to the housing of the ball-joint case and to the locking ring,the ball joint according to the invention can be made not only withoutradial or axial play, but also with predefined damping, and thereforewith wear reduced to the minimum throughout the entire life of the balljoint.

What is claimed is:
 1. A ball joint, especially a motor-vehicle steeringor suspension ball joint, comprising a pivot provided with a sphericalhead, a ball-joint case provided with a housing to receive the pivothead, and a bearing shell of plastic material interposed between thepivot head and the case housing, wherein the bearing shell of the balljoint comprises a one-piece molded cup, closed at a bottom side andprovided, by molding, with a spherical inside surface extending over asolid angle corresponding to more than one hemisphere, with a circularorifice, whose diameter is smaller than a diameter of the sphericalinside surface and which is disposed opposite the bottom side, and witha plurality of rupture zones of small thickness distributed over acircumference of the orifice, while extending from the orifice toward anequatorial plane of the spherical inside surface disposed parallel to aplane of the said orifice, the rupture zones having a conformation thateach undergoes predefined rupture into two sections during a firstexpansion of the orifice and that, after insertion of the head of thepivot into the bearing shell, elastic constriction of the orifice ispermitted together with exact repositioning of the two sections of eachrupture zone around the pivot head.
 2. A ball joint according to claim1, wherein the rupture zones have a conformation such that each givesrise to a rupture along a predefined line of weakness.
 3. A ball jointaccording to claim 2, wherein the line of weakness has a zig-zag shape.4. A ball joint according to claim 1, wherein the bearing shell isprovided on the outside, in an equatorial zone, with a cylindrical part,which toward the bottom side is followed by a substantially conicalpart, and in that the housing of the case is provided with a cylindricalpart followed by a substantially conical bottom part.
 5. A ball jointaccording to claim 4, wherein the conical part of the bottom of thehousing of the case comprises a frustoconical outside zone, with a taperangle larger than a taper angle of the conical outside part of thebottom zone of the bearing shell and a conical central inside zone witha taper angle smaller than a taper angle of the conical outside part ofthe bearing shell.
 6. A ball joint according to claim 5, wherein thebearing shell is provided, between its cylindrical outside part and itsorifice, with a frustoconical outside part followed at a level of theorifice by an outside shoulder, and in that the ball joint additionallycomprises a locking ring provided with a frustoconical inside surfacecorresponding to the frustoconical outside part of the bearing shell,and which, after insertion of the head of the pivot into the bearingshell, can be interlocked behind the shoulder of the bearing shell tomaintain the assembled pivot and bearing shell in a form of a moduleconfigured to be mounted in the ball-joint case and of being fixedtherein.
 7. A process for manufacture of a ball-joint bearing shellaccording to claim 1, wherein the bearing shell is molded between afixed mold part whose cavity corresponds at least to the bottom part ofthe bearing shell, at least one movable mold part whose cavitycorresponds at least to the orifice part of the bearing shell, and amovable core with a spherical head, whose shape correspondssubstantially to a shape of the spherical head of the pivot of the balljoint, wherein, to remove the bearing shell from the mold, there aresuccessively displaced a) the movable mold part, to release the orificepart of the bearing shell, or in other words the part comprising therupture zones, toward the outside, and b) the movable core, to extractthe spherical head of the bearing shell on the orifice side, whilecausing well-defined rupture of the said rupture zones by expansion ofthe orifice part of the bearing shell.
 8. A process according to claim7, wherein the bearing shell is blocked in the fixed part of the moldduring extraction of the spherical head of the core.